1. Field of the Invention
This invention is directed to electronic ballast systems for gas discharge tubes. In particular, this invention is directed to automatic gain control ballast systems for fluorescent tubes. In particular, this invention is related to electronic ballast systems which are current driven and provide for automatic gain control. More in particular, this invention relates to a ballast system which provides for a frequency control mechanism utilizing inductance characteristics of an inverter transformer to allow for substantial frequency stabilization. Still further, this invention directs itself to an electronic ballast system for fluorescent light tubes which maximizes the operating lifetime of the fluorescent tubes while maintaining a circuit simplicity with a minimum number of electrical components contained within the ballast system circuit.
2. Prior Art
Electronic ballast systems for gas discharge tubes are known in the art. However, in some prior art electronic ballast systems, there is no provision made for frequency stabilization of the circuit. Thus, in such prior art electronic ballast systems, when a gas discharge tube is removed from the circuit, there is a deleterious flickering of the remaining gas discharge tubes, or in some cases, a complete breakdown of the visible light from the remaining gas discharge tubes.
In other prior art electronic ballast systems, a large number of electrical components are utilized to maintain the gas discharge tubes in operation. However, such large numbers of electrical components increase the manufacturing costs of the prior art electronic ballast systems and further reduce the reliability of such ballast systems.
In other prior art electronic ballast systems, unwanted effects are caused by the amplitude of a multiplicity of harmonic frequencies coupled into the DC supply of such prior art systems. In such prior art electronic ballast systems, correction circuits are not provided to reduce such harmonic frequencies which causes disadvantageous voltage signals applied to the ballast circuitry. In other prior art electronic ballast systems, a saturating transformer is driven by the magnitude of a feedback voltage. In such prior art electronic ballast systems, the oscillation frequency is highly dependent on the supply voltage and thus, where voltage surges are produced, there is a non-constant light output from the gas discharge tubes and variations in the supply voltage may also cause flickering.
In other prior art electronic ballast systems, inverter transformer secondary windings are wound in opposing directions with respect to the primary winding. Thus, in such prior art electronic ballast systems, the inverter transformers are more difficult to manufacture, and therefore more costly and less reliable.